I know in person someone playing in the Polish highest division, not exactly a beer league. Eventually the club got rid of him for disciplinary reasons - the physios didn't approve him training his upper body too muscular that makes you less 'elastic'. He obviously didn't agree with them but by looking at his career trajectory they were probably right.

They're wrong. The reason that every athlete should train every part of their body is because it raises overall testosterone and promotes blood flow throughout the entire body, which speeds development and healing of the muscle groups that are predominantly used in whatever sport... e.g. I'm a sprinter, so I train my upper body as well because it helps my legs grow and heal faster.

Many competitive sports have requirements to be unbalanced for weight reasons.

E.g. pro cyclists have to avoid any upper body activities like swimming since they'll put on upper body mass that hurts their performance; the opposite is pro climbers where training quads will lower the performance since they'll grow extra leg mass that arms will have to lift.

That’s true to a degree for cyclists but depends on which discipline and what their objectives are.

A time trialist or sprinter would be much less concerned about upper body weight than a pure climber.

Even when he was as shedding weight for the Tour, Wiggins was was still doing dead lifts (with a low weight) and other upper body exercises because having a strong core is very useful.

You're correct. They didn't mean he can't train upper body but there are limits to upper body mass. A bodybuilder doesn't make a good footballer.

Robert Lewandowski is very fit and strong from top to bottom. I'm surprised Polish clubs aren't encouraging their players to imitate him.

Not everyone should be a "bomber" n.9 like Lewa...